Pipelaying vessel and a method of converting a maritime vessel to a pipelaying vessel

ABSTRACT

A reel pipelaying vessel of the type having a main pipeline reel (118) mounted for rotation about a horizontal axis, a variable angle pipeline launching ramp (128) having pipeline straightening and tensioning means mounted thereon and having: an improved pipeline launching ramp arrangement including rack and pinion elevator means (140, 142, 144); an improved level winding mechanism for translating the pipeline straightening and tensioning means as the pipe is spooled onto or unspooled from the reel; sea fastening means for restraining axial movement of the reel while the vessel is in transit, thereby increasing the maximum pipeline load for reel bearings (114, 116) of a given load capacity; sponsons (108, 110) for providing additional flotation and strengthening the hull; an improved arrangement of auxiliary reels (120); a cantilever structure (200) for guiding auxiliary lines, providing access to the main reel and protecting the bridge (218) of the vessel; improved pipeline abandonment and recovery arrangements; an improved reel structure; and an improved pipeline clamping arrangement. A method of converting an existing vessel to a reel pipelaying vessel is also described.

This invention relates to a pipelaying vessel, and more specifically butnot exclusively relates to a self-propelled and dynamically-positionedreel pipelaying ship in which a pipe-spooling reel and associated pipehandling equipment are integrated into the structure of the ship. Insome embodiments of the pipelaying ship, there is provision for thesimultaneous laying of a plurality of pipes, or the simultaneous layingof one or more pipes together with one or more cables.

In prior-art pipelaying vessels as employed in laying offshore subseapipelines for such uses as the gathering of oil and/or gas from offshoresubsea wells, as, for example, in the Gulf of Mexico, it has beenconventional to use one of two main methods to lay the pipe. In thefirst, or "stovepiping", method, a pipeline is fabricated on the deck ofa lay barge by welding together individual lengths of pipe as the pipeis paid out from the barge. Each length of pipe is about 40 feet or 80feet long. Thus, the pay-out operation must be interrupted periodicallyto permit new lengths of pipe to be welded to the string. Thestovepiping method requires that skilled welders and their relativelybulky equipment accompany the pipelaying barge crew during the entirelaying operation; all welding must be carried out on site and oftenunder adverse weather conditions. Further, the stovepiping method isrelatively slow, with experienced crews being able to lay only one ortwo miles of pipe a day. This makes the entire operation subject toweather conditions which can cause substantial delays and make workingconditions quite harsh. (A modification of the stovepiping techniqueknown as the "J-lay" technique allows the laying of pre-assembledpipestrings up to 240 feet in length, but pipelaying is stilldiscontinuous).

The other principal conventional method is the reel pipelayingtechnique. In this method, a pipeline is wound on the hub of a reelmounted on the deck of a lay barge. Pipe is generally spooled onto thereel at a shore base. There, short lengths of pipe can be welded underprotected and controlled conditions to form a continuous pipeline whichis spooled onto the reel. The lay barge is then towed to an offshorepipelaying location and the pipeline spooled off the reel betweencompletion points. This method has a number of advantages over thestovepiping method, among them, speed (up to one mile per hour); loweroperating costs (eg smaller welding crews and less welding equipmentmust be carried on the lay barge); and less weather dependency.

Historically, the technique of laying undersea fluid-carrying pipelineshad its rudimentary beginnings in England in the 1940's in a War-timeproject known as "Operation Pluto". In the summer of 1944, 3-inchnominal bore steel tubes, electrically flash-welded together, werecoiled around floating drums. One end of the pipe was fixed to aterminal point; as the floating drums were towed across the EnglishChannel, the pipe was pulled off the drum. In this manner, pipelineconnections were made between the fuel supply depots in England anddistribution points on the European continent to support the Alliedinvasion of Europe. (See Blair, J S, "Operation Pluto: The Hamel SteelPipelines", Transactions of the Institute of Welding, February 1946).

The broad concept of reel pipelaying was also disclosed in BritishPatent No. 601,103 wherein it was suggested that lengths of pipe can bejoined together at the manufacturing plant and coiled onto a drum,mounted on a barge or ship; the loaded barge would then be moved to thedesired marine location and the pipe unwound from the drum by fixing oneend of the pipe and towing the barge away from the fixed location.

While the concepts described in British Patent No. 601,103 and thoseactually used in Operation Pluto were adequate for wartime purposes, noknown further development work or commercial use of the technique oflaying pipe offshore from reels was carried out after World War II.After a hiatus of about fifteen years, research into the reel pipelayingtechnique was renewed and was carried on by Gurtler, Herbert & Co, Incof New Orleans, La. (USA); by 1961, Gurtler, Herbert had sufficientlyadvanced the reel pipelaying technique to make it a commerciallyacceptable and viable method of laying pipe for the offshore petroleumindustry, able to compete with the traditional stovepiping technique.The first known commercial pipelaying reel barge, called the U-303, wasbuilt by Aquatic Contractors and Engineers, Inc, a subsidiary ofGurtler, Herbert, in 1961. The U-303 utilised a large vertical-axisreel, permanently mounted on a barge and having horizontally orientatedflanges (generally referred to in the trade as a "horizontal reel"). Acombined straightener/level winder was employed for spooling pipe ontothe reel and for straightening pipe as it was unspooled. The U-303 firstlaid pipe commercially in September 1961, in the Gulf of Mexico off thecoast of Louisiana and was used successfully during the 1960's to layseveral million linear feet of pipe of up to 6 inches diameter. TheU-303 reel pipelaying barge is described in U.S. Pat. No. 3,237,438(Tesson) and U.S. Pat. No. 3,372,461 (Tesson).

The successor to the U-303, currently in use in the Gulf of Mexico andknown in the trade as the "Chickasaw", also utilises a large horizontalreel, permanently mounted on the barge such that it is not readilymovable from one carrier vessel to another. Various aspects of"Chickasaw" are described in the following U.S. Patents:

Sugasti, et al--U.S. Pat. No. 3,630,461

Gibson--U.S. Pat. No. 3,641,778

Mott et al--U.S. Pat. No. 3,680,432

Key et al--U.S. Pat. No. 3,712,100

Commercial reel pipelaying techniques require the use of certain pipehandling equipment in addition to the reel. Among such pipe handlingequipment essential to any commercial reel pipelaying system is astraightener mechanism. This may take the form of a series of rollers ortracks, or any other arrangement which imparts sufficient reversebending force to the pipe to remove residual curvature such that afterunspooling, the pipe will lay substantially straight on the sea bottom.No such pipe-conditioning apparatus was used in "Operation Pluto" orcontemplated in the British Patent No. 601,103.

U.S. Pat. Nos. 3,982,402 and RE30486 (Lang et al) describe an apparatusfor laying pipe from a vertical reel in which the pipe conditioningapparatus is pivotable to adjust the lift-off angle of the pipe relativeto the horizontal (eg the deck of a ship) as a function of the waterdepth in which the pipe is being laid. This has distinct commercialadvantages, especially where the reel pipelaying system is incorporatedinto a self-propelled ship capable of travelling to different job sites,having different pipe size and/or lay depth requirements.

An early concept for a reel pipelaying ship is described in Goren, etal, "The Reel Pipelay Ship--A New Concept", Offshore TechnologyConference Proceedings, May 1975 (Paper No OTC 2400). This paper(hereinafter the Goren, et al 1975 OTC Paper) described advantages andoperating features of a proposed reel pipelaying ship. However, the costof construction of a ship as described there was estimated to be of theorder of $100,000,000.

The research and development work for the ship described in the Goren,et al paper was subsequently materially revised in numerous majorrespects, and substantial changes and improvements were made to achievethe design of a substantially different reel pipelaying ship which isdescribed in the following U.S. Pat. Nos.:

Springett, et al--U.S. Pat. No. 4,230,421

Uyeda, et al--U.S. Pat. No. 4,269,540

Yenzer, et al--U.S. Pat. No. 4,297,054

Springett, et al--U.S. Pat. No. 4,340,322

Uyeda, et al--U.S. Pat. No. 4,345,855

The vessel described in these Patents was constructed and is currentlyin use in various offshore oil fields, being known in the offshore oilindustry as the "Apache" (now re-named the "Stena Apache"). This vesselis a self-propelled dynamically-positioned reel pipelaying ship whichhas a specially constructed hull comprising a reel support structure forrotatably mounting a vertical reel for unspooling a rigid-walledpipeline. Only a single pipeline was originally handled by this ship,though the "Apache" was subsequently modified by the addition of anauxiliary reel positioned forward of the main reel to enable the layingof "piggyback" lines strapped to the main pipeline. Other pipe handlingequipment includes a pipe bending radius controller; pipe straighteningequipment; clamping assemblies; a stern pipe guide assembly and a levelwind assembly. A tensioning assembly is also arranged on a support rampassembly. The pipe exit angle or the water entry angle is from 18° toabout 60° since this is the range of angular movement of the supportramp assembly. The upper part of this range of the pipe water entryangles is sufficient to accommodate laying a single pipeline inapproximately 3,000 feet water depth. In order to lay pipe at greaterdepths it is necessary to increase the pipe water entry angle.

The "Stena Apache" vessel is not equipped to lay multiple lines since ithas but a single main reel and does not have adequate unused deck spaceto permit the convenient placement of auxiliary reels. An earlysuggestion which was made during the vessel's construction phase andmentioned in the above Patents, was that portable reels could be placedon the "Apache" deck to permit stern bundling of smaller lines with thepipeline from the main reel. These smaller lines were not required to bepassed through the pipe handling equipment with the main reel pipelineaccording to the suggestion and there were no operative disclosures asto forming a juxtaposed plurality of operational lines by contact with alaying device which is adapted to move all the lines at a commonvelocity. This stern bundling suggestion was made in the OTC Paper No.3069, May 8-11, 1978.

There are increasing requirements in the offshore petroleum industry forlaying single or multiple operational lines in deep water at depthsgreater than 3,000 feet and in remote areas far from supply bases. To becommercially viable a pipelaying vessel should preferably also becapable of laying either single or multiple operational lines in shallowwaters of less than 2,000 feet up to 3,000 feet depth. The reelpipelaying vessel of this invention (as defined below) represents a newand different concept for meeting these needs.

It is also desirable that the stern deck space around the pipelayingequipment be more easily and safely accessible.

While it is technically feasible to design and build a ship specificallyto provide several or all of the abovementioned desirable features, sucha ship would be relatively expensive. On the other hand, there are manysea-going vessels that are currently surplus to requirements and henceavailable at relatively low cost such that the cost of conversion toreel-lay capacity is potentially more economical than new-build.However, selection of a vessel to be modified, and the actualmodification procedures, require to be individually and collectivelycontrolled in non-obvious ways to avoid excessive costs andunsatisfactory results.

Certain aspects of the present invention will also be shown to beapplicable to new-build vessels, and/or to retrofitting/upgrading anexisting pipelaying vessel.

According to a first aspect of the present invention there is provided areel pipelaying vessel, said vessel being fitted with a dynamicpositioning system (DPS), said vessel being provided with a reel-holdingwell at a location amidships, said vessel being provided withreel-mounting bearings on laterally opposite sides of said well, andsaid vessel being provided with ramp-mounting bearings at a sternwardslocation on said vessel for the mounting of a pipe-launching rampthereon.

Said vessel is preferably formed with a hull and may be provided withsupplementary flotation means which preferably comprises hull-contiguoussponsons. Such sponsons may extend along at least a greater part of thelength of the hull. Said sponsons are preferably so formed and attachedto the hull as to constitute longitudinal strengthening members for thevessel to assist the vessel to withstand loads imposed in use of thevessel through said reel-mounting bearings.

Said reel pipelaying vessel preferably further comprises a pipe-spoolingreel temporarily or permanently rotatably mounted on said reel-mountingbearings. Said pipe-spooling reel preferably includes first and secondlateral side portions each comprising a central rotary bearing, aplurality of radial spokes extending outwardly from said central rotarybearing and a main flange surface connecting at least the outer portionsof said spokes, the reel further including a hub surface connecting saidlateral side portions such that said reel, in radial cross-section, hasa portal frame configuration, there being no central shaft connectingthe rotary bearings of the respective side portions.

Said reel pipelaying vessel preferably further comprises apipe-launching ramp temporarily or permanently mounted on saidramp-mounting bearings. The mounting of said ramp is preferably arotational mounting whereby the elevation of the ramp with respect tothe vessel is variable, said vessel preferably further comprising rampelevation control means for controllably varying the elevation of theramp. Said ramp elevation control means preferably comprisesvariable-length ramp support means anchored at or adjacent one endthereof upon fixed structure of the vessel and at or adjacent the otherend of a variable length portion of the support to the ramp at alocation thereon not adjacent said rotational mounting of said ramp.Said variable-length ramp support means preferably comprises a pair ofrack and pinion elevators located one on each side of said ramp andconjointly operable to vary the elevation of said ramp with respect tosaid vessel.

Said pipe-launching ramp preferably comprises a pipe radius controlmeans for imparting a substantially uniform radius of curvature to alength of pipe de-spooled from said reel in pipelaying operation of saidvessel.

Said pipe-launching ramp preferably comprises level-wind means foraccommodating variations in the lateral positioning of a length of pipespooled onto said reel as a plurality of side-by-side turns, duringspooling and de-spooling of said length of pipe. Said level-wind meansand said pipe radius control means are preferably mounted and controlledfor conjoint lateral movement, preferably by said pipe radius controlmeans being mounted upon said level-wind means for carriage thereby.

The combination of said pipe-launching ramp and said ramp-mountingbearings is preferably such that the underside of said pipe-launchingramp is clear of underlying deck of the reel pipelaying vessel, at leastbetween said ramp-mounting bearings and such part or parts of the deckat which ramp elevation control means is anchored. The deck to rampunderside clearance is preferably at least sufficient to constitutewalk-under headroom. Within said combination, said ramp-mountingbearings are preferably arranged to dispose a horizontal pivot axis forthe ramp substantially above said underlying deck whereby thus toprovide at least the greater part of said clearance.

Said reel pipelaying vessel may be provided with one or more auxiliaryreels for the spooling/de-spooling of cable(s) and/or auxiliary pipe(s),the auxiliary reel(s) preferably being laterally aligned with the mainpipe reel, and conveniently located substantially on the longitudinalcentre-line of the vessel fore and/or aft of the main pipe reel. Wherethe auxiliary reel or at least one of the auxiliary reels carries or isintended to carry a plastically deformable auxiliary pipe or cable, thepipe-launching ramp may be formed with or provided with a respectiveauxiliary radius control means for imparting a substantially uniformradius of curvature to said auxiliary pipe or cable. Where at least oneauxiliary reel is located forward of the main pipe reel, said pipelayingvessel may be provided with a fixed cantilever or other bridgingstructure leading auxiliary pipe/cable to/from the auxiliary reel(s)from/to the pipe-launching ramp in a path extending over and clear ofthe path of pipe between said ramp and the main reel. Said fixedcantilever or other bridging structure is preferably provided with anarray of rollers or other suitable means for facilitating passage of theauxiliary pipe/cable thereover.

Said reel pipelaying vessel is preferably provided with restraint meansselectively operable on at least the main pipe reel to provide at leastlateral restraint of said main reel while said main reel is not requiredto rotate, whereby to relieve the reel bearings of at least some lateralloading when said restraint means is applied. Said restraint meanspreferably comprises an array of chocks which can be selectively pressedagainst or retracted from opposite sides of the reel on either side ofthe rotation axis thereof whereby selectively to apply lateral clampingforces on the reel. Each chock preferably comprises a hydraulicallyextendable strut lockable in its extended condition by means of ascrew-threaded fastener. Each said chock is preferably anchored at oneend thereof to the reel-holding well and/or to vessel decking adjacentthereto, and each said chock is preferably provided at the other endthereof with a reel-contacting surface of reduced friction, for examplea bronze pad.

The reel pipelaying vessel is preferably further equipped with anabandonment and recovery system (A&R system) comprising awinch/wire/sheave arrangement extending a haulage wire (or rope, chain,or cable) from a suitably located winch by way of one or more sheaves toextend down the pipe-launching ramp so as to enable the end of a pipebeing laid to be let overboard in a controllable fashion, and tofacilitate the pulling on-board of a pipe end. The winch haulage drum ispreferably anchored within the vessel. The sheave arrangement preferablyincludes one sheave located adjacent the ramp-mounting bearings to givethe A&R system a measure of level luffing, and at least one furthersheave disposed on the ramp at a location substantially displaced fromthe sternwards end of the ramp to bring the haulage wire into a pathextending down the ramp from said location on the ramp. The sheavespreferably have articulated anchorage to cope with level windingtraverses and variable ramp elevations. The sheaves are preferablywide-bodied to allow the passage of wire rope fittings and shacklesincorporated into the A&R system.

The vessel preferably further includes pipeline clamping means locatedadjacent the aft end of a pipeline launching ramp, said clamping meanscomprising

at least a first clamp of generally cylindrical configuration mounted onsaid ramp by clamp mounting means, said first clamp comprising first andsecond semi-cylindrical portions hinged together along their lengths ona side of the clamp disposed below the pipeline path.

Preferably also, said clamp mounting means is adapted to be retractablesuch that said first clamp may be retracted to a position below thepipeline path when not in use.

Preferably also, said clamp mounting means has a load capacity greaterthan the load capacity of said first clamp, whereby the clamp loadcapacity may be increased up to the capacity of said clamp mountingmeans by securing one or more additional clamps to the pipeline inabutment with the first clamp and upstream therefrom in the direction ofpipeline unspooling.

According to a further aspect of the present invention there is provideda pipe-launching ramp, said ramp comprising a planar frame havingbearing means at or towards one end thereof for rotatably mounting theramp on ramp-mounting bearings of a pipelaying vessel, and couplingmeans located at or towards the other end of the frame for coupling ofthe ramp to a ramp elevation control means for controllably varying theelevation of the ramp.

Preferably, said ramp elevation control means comprises variable-lengthramp support means adapted to be anchored at or adjacent one end thereofupon fixed structure of the vessel and at or adjacent the other end of avariable length portion of the support to the ramp at a location thereonnot adjacent said rotational mounting of said ramp.

Preferably also, said variable-length ramp support means comprises apair of rack and pinion elevators located one on each side of said rampand conjointly operable to vary the elevation of said ramp with respectto said vessel.

Preferably also, said pipe-launching ramp comprises a pipe radiuscontrol means for imparting a substantially uniform radius of curvatureto a length of pipe de-spooled from said reel in pipelaying operation ofsaid vessel.

Preferably also, said pipe-launching ramp comprises level-wind means foraccommodating variations in the lateral positioning of a length of pipespooled onto said reel as a plurality of side-by-side turns, duringspooling and de-spooling of said length of pipe.

Preferably also, said ramp includes at least two levelwind-mountingcrossbeams; said levelwind means comprising a rectangular latticemounted for lateral movement on said crossbeams, lateral movementcontrol means for laterally moving said lattice on said crossbeams,radius control means carried on said lattice for imparting a uniformcurvature to a pipe being de-spooled over said ramp, and pipe grippingmeans carried by said lattice for gripping a pipe being de-spooled oversaid ramp to apply straightening and/or tensioning forces to said pipe.

As compared to the pipe-launching ramps described in WO93/06401 andWO93/06402 wherein a flexible levelwind is mounted on five transverserails on a wide stiff truss, in the present invention the levelwind isconstructed as a stiff rectangular lattice running on two crossbeamscarried by a ramp which is simply a planar frame, this arrangement beinglighter than the abovementioned prior art for a given load capacity.

The levelwind lattice can be boxed in or surrounded to provide fullweather protection, and is preferably equipped with a dualbulkhead/platform system to provide a working location which allowspersonnel to work on the lattice whether the ramp is near horizontal ornear vertical. Access to the working location can be by a ladder systemon one side of the levelwind and/or by a man-carrying lift on the otherside of the levelwind.

The radius control means and the pipe gripping means can be as describedin the abovementioned PCT publications, but a preferred ramp elevator inaccordance with part of the present invention, for controllably varyingthe inclination of the ramp, is very different in that the preferredramp elevator has its lower end(s) at a fixed location(s) on the vesselrather than travelling along deck rails in the above PCT publications;this arrangement of the present invention concentrates ramp-elevatingloads at discrete points, thereby minimizing the required extent ofunder-deck stiffening and hence cost.

According to a further aspect of the present invention there is provideda reel-clamping chock for clamping a pipe-carrying reel against movementthereof in an axial direction, said chock comprising a power-extendablejack, selectively operable locking means for locking said jack in anextended configuration thereof, coupling means at one end of the chockfor coupling that end of the chock to an anchorage, and reel-contactingmeans at the other end of the chock for the application of jacking forceto said reel.

Said power-extendable jack is preferably a hydraulic jack, convenientlyrealised as a piston and cylinder assembly.

Said selectively operable locking means is preferably a screw-threadednut or an internally screw-threaded ring which can be screwed along onepart of said jack, after extension of said jack, to bear against anotherpart of said jack which has been extended relative to said one partwhereby to lock said two parts against relative movement tending toreverse such extension.

Said reel-contacting means preferably comprises a friction-reducingmeans for contacting the reel in use of the chock. The friction-reducingmeans preferably comprises a bronze pad attached to or integral withsaid other end of the chock.

According to a further aspect of the present invention there is provideda reel-clamping chock array, said array comprising at least fourreel-clamping chocks according to the previous aspect of the presentinvention, disposed so that a respective plurality of said chocks isextendable to contact each of the axially opposite ends of the reel,with at least one chock in each said plurality being disposed to beextendable to contact the respective end of the reel at a locationthereon which is substantially diametrically opposite to a location onthat end of said reel to which at least one other chock in the sameplurality is extendable to contact that end of said reel, whereby saidarray may be operated in a manner to reduce or eliminate skewing forcesimposed on said reel by application thereto of reel-clamping forces.

According to still another aspect of the present invention there isprovided a combined pipe and/or cable bridge and personnel accessgangway for fitting to a reel pipelaying vessel having a main pipe reeland an auxiliary pipe/cable reel located ahead of the main reel, saidcombined bridge/gangway comprising a cantilever support whose forwardend is mountable at a location on said vessel intermediate said mainreel and said auxiliary reel, such that said combined bridge/gangwayextends rearward of said location towards and partly overlapping saidmain reel at an elevation with respect thereto that will carry auxiliarypipe and/or cable being unspooled from said auxiliary reel over saidmain reel and over pipe being unspooled from said main reel, saidcombined bridge/gangway having a longitudinally extending pipe transportmeans for carrying auxiliary pipe/cable thereover, said combinedbridge/gangway further having a longitudinally extending walkwaydimensioned and arranged for carrying pedestrians from said location orfrom near thereto at least to a point over said main reel.

Said combined bridge/gangway can be incorporated into a new-build reelpipelaying vessel or into the conversion of a maritime vessel to a reelpipelaying vessel, or said combined bridge/gangway can be provided asequipment for retrofitting onto an existing reel pipelaying vessel.

Said pipe transport means may comprise a longitudinally extending arrayof pipe/cable carrying rollers, or a longitudinally extending pipe/cableconveyor belt or chain.

The mounting of said cantilever support may be such that the generalinclination of said combined bridge/gangway in a longitudinal directionis either fixed or controllably variable.

According to still another aspect of the invention, there is provided apipe-spooling reel for use in laying pipe from a reel pipelaying vessel,including first and second lateral side portions each comprising acentral rotary bearing, a plurality of radial spokes extending outwardlyfrom said central rotary bearing and a main flange surface connecting atleast the outer portions of said spokes, the reel further including ahub surface connecting said lateral side portions such that said reel,in radial cross-section, has a portal frame configuration, there beingno central shaft connecting the rotary bearings of the respective sideportions.

According to still another aspect of the present invention there isprovided a method of converting a maritime vessel to form at least thebasis of a reel pipelaying vessel, said method comprising the steps ofselecting a maritime vessel which either already has a dynamicpositioning system (DPS) or is capable of being fitted with a DPS,providing said maritime vessel with a reel-holding well at a locationamidships, providing said maritime vessel with reel-mounting bearings onlaterally opposite sides of said well, and providing said maritimevessel with ramp-mounting bearings at a sternward location for themounting of a pipe-launching ramp thereon.

The step of providing said maritime vessel with a reel-holding well at alocation amidships may comprise a combination of the sub-steps oftransversely dividing the maritime vessel at a selected locationthereon, into a bow section and a stern section, mutually separating thebow section and the stern section, providing a reel-holding well sectionhaving a transverse cross-section substantially matching the transversecross-section of the maritime vessel at said selected location thereon,placing the reel-holding well section between the bow section and thestern section, bringing the three said sections together and mutuallysecuring them to form at least the basis of a reel pipelaying vesselhaving a substantially continuous hull line.

The maritime vessel may be provided with supplementary flotation means,preferably by the addition of laterally mounted sponsons which mayextend for a substantial fraction of the total length of the reelpipelaying vessel. The sponsons are preferably integrated withunderlying portions of the original hull of the maritime vessel, and thesponsons preferably extend upwardly at least sufficiently to ensure thatthe heeling limit of the reel pipelaying vessel is not substantiallyless than the heeling limit of the maritime vessel prior to conversionthereof.

Said method preferably comprises the further steps of providing saidmaritime vessel with a DPS if it does not already possess a DPS,providing a pipe-spooling reel and rotatably mounting said reel on saidreel-mounting bearings, and providing a pipe-launching ramp and mountingsaid ramp on said ramp-mounting bearings. Said vessel is preferablyfurther provided with ramp elevation control means for controllablyvarying the elevation of the ramp.

Said maritime vessel may be a diving support vessel (DSV) or any otherform of maritime vessel suitable for conversion to a reel pipelayingvessel in accordance with the present invention, such a convertiblemaritime vessel including but not being restricted to any known form ofmaritime vessel constructed or adapted for pipelaying whether by reelpipelaying or otherwise.

Embodiments of the invention will now be described by way of example,with reference to the accompanying drawings wherein:

FIG. 1 is a starboard elevation of a reel pipelaying vessel inaccordance with the present invention;

FIG. 2 is a plan view of the vessel of FIG. 1;

FIG. 3 is a starboard elevation (to an enlarged scale) of the stern areaof the vessel of FIG. 1 with a pipe-launching stern ramp to its lowestelevation;

FIG. 4 is a stern view corresponding to FIG. 3;

FIG. 5 is a view corresponding to FIG. 3 but with the ramp at itshighest elevation;

FIG. 6 is a stern view corresponding to FIG. 5;

FIG. 7 is a starboard elevation of another form of reel pipelayingvessel in accordance with the present invention;

FIG. 8 is a plan view of the main deck of the vessel of FIG. 7, ie, viewwith the vessel bridge and upper decks removed;

FIG. 9 is a starboard elevation of a modified version of thepipe-launching ramp and associated equipment forming part of the vesselof FIG. 7;

FIG. 10 is a starboard elevation of ramp-mounting bearings and a rampelevation controller associated with the ramp of FIG. 9;

FIG. 11 is a front elevation of the arrangement of FIG. 10;

FIG. 12 is a view from the starboard side of the reeving arrangement ofan abandonment and recovery system (A&R system) associated with the rampof FIG. 9, shown with the ramp at its minimum elevation;

FIG. 13 is a view from above of the arrangement of FIG. 12, as seen fromthe direction of the arrow "P" in FIG. 12;

FIG. 14 is a cross-section of part of the arrangement of FIG. 12, takenon the line A--A in FIG. 12;

FIG. 15 is a view corresponding to FIG. 12 but with the ramp at itshighest elevation;

FIG. 16 is a longitudinal section of a reel-clamping chock for use withthe present invention;

FIG. 17 is an outside end view of the arrangement of FIG. 16, as viewedin the direction of the arrow "P" in FIG. 16;

FIG. 18 is an inside end view of the arrangement of FIG. 16, as viewedin the direction of the arrow "Q" in FIG. 16;

FIG. 19 is a plan view, to a much-reduced scale, of a reel-clampingchock array applied to a reel;

FIG. 20 is a side view of a preferred embodiment of a main reel for usewith the vessel of FIGS. 1 to 19;

FIG. 21 is a sectional view on line A--A of FIG. 20;

FIG. 22 is a sectional view on line B--B of FIG. 20;

FIG. 23 is a sectional view on line C--C of FIG. 20;

FIG. 24 is a view similar to FIG. 23, showing a modified chockingarrangement;

FIGS. 25(a), (b) and (c) are schematic illustrations of a preferredarrangement of a main pipeline clamp; and

FIG. 26 is a schematic illustration of a particularly preferredarrangement of pipeline clamps.

Referring first to FIGS. 1 and 2, these show respectively starboard andplan views of a reel pipelaying vessel 100 which is similar in certainrespects to known forms of reel pipelaying vessels, for example asdisclosed in WO93/06401 and WO93/06402. However, general and particularaspects of the vessel 100 are distinctively different from the priorart, as will be detailed below.

The vessel 100, to be known as the "Stena Apache Two", is intended to beconverted from the diving support vessel (DSV) "Stena Wellservicer" (notseparately illustrated) by the method now to be described.

The method provides that the DSV will be transversely dividedimmediately astern of the forward bridge and accommodation section 102,and the sternwards section 104 separated from the forward section 102. Aprefabricated hull section 106 will next be located between the forwardand sternwards sections 102 and 104, and the three sections then weldedtogether to form the basis of a vessel with an extended hull. Port andstarboard sponsons 108 and 110 are subsequently attached to the outsideof the vessel hull from the stern to about the middle of the forwardsection 102 so as to increase the displacement of the resultant vessel100, and hence increase the vessel's load-carrying capacity. Thesponsons 108 and 110 are also designed and attached such as to increasethe longitudinal bending strength of the vessel 100.

The hull section 106 is formed with a reel-holding well 112. Bearingpedestals 114 and 116 are fabricated on port and starboard sides of thewell 112 to form reel-mounting bearings. A main pipe-carrying reel 118is rotatably mounted in the bearings 114 and 116. A main reel drivingand braking system (not shown) is installed in the well 112.

A large auxiliary reel 120 is installed immediately forward of the mainreel 118, in the redundant DSV dive system garage in the after end ofthe forward section 102. The large auxiliary reel 120 is intended tocarry cable(s) and/or auxiliary pipes.

A small auxiliary reel 122 is installed immediately aft of the main reel118, in the redundant DSV gas storage area in the forward end of thesternwards section 104. The small auxiliary reel 122 is intended tocarry cable(s) and/or hose(s).

The stern of the vessel 100 is provided with substantially elevated rampmountings 124 and 126. A ramp 128 in the form of a rectangular latticehas its rear end 130 rotatably mounted on the upper ends 132 and 134 ofthe ramp mountings 124 and 126 (see FIGS. 4 and 6).

The mountings 124 and 126 are not only shaped and dimensioned to supportthe ramp 128 on their upper ends 132 and 134 substantially above thevessel's main deck 136 such as to leave walk-through headroom under theramp 128, but also to locate their upper ends 132 and 134 clear of thestern of the vessel 100 such as to enable pipe to be launched aft theramp 128 at a near-vertical angle (see FIG. 5).

The forward end 138 of the ramp 128 is supported at a controllablyvariable height above the deck 136 by means of a ramp elevationcontroller 140 comprising a pair of rack and pinion elevators 142 and144.

Referring to FIGS. 9 and 10, each of the ramp elevators 142 and 144comprises an elongate rack 146 with a row of teeth along both edges, theracks 146 each being tiltably mounted on the deck 136 by means of arespective hinge 148. The use of deck-fixed hinges 148 allows thenecessary reinforcements of the deck 136 to be limited to the tworelatively small areas under the hinges 148, in contrast to thewidespread deck reinforcement required with prior art ramp elevators(eg, the rail-mounted ramp elevators of WO93/06401 and WO93/06402).

Each of the ramp elevators 142 and 144 further comprises a power-drivenpinion assembly 150 comprising a pinion frame 152 mounting three pairsof pinions 154, with one pinion of each pair engaging one of the rows ofteeth on either edge of the rack 146. Each of the pinions 154 is drivenby a respective hydraulic motor and reduction gear unit 156. Therespective upper ends of the two pinion assemblies 150 are pivotallycoupled to the forward end 138 of the ramp 128 by respective pivotcouplings 158. The pinion assemblies 150 are also mutually cross-linkedby a transverse frame 159.

Conjoint operation of the hydraulic drive units 156 causes the pinionassemblies 150 to crawl up/down the racks 146 hence to raise/lower theforward end 138 of the ramp 128. Control of the drive units 156 is suchas to ensure (as far as possible) synchronous movement of the assemblies150 and hence to avoid movement-induced distortion of the ramp 128(whose structure is lighter and less rigid than the structures of theramps described in WO93/06401 and WO93/06402). Positive synchronisationof the movements of the two pinion assemblies 150 can optionally beensured by cross-linking at least one pinion in one assembly 150 withthe corresponding pinion in the opposite assembly 150 by means of atransverse drive shaft (not illustrated) in addition to or as asubstitute for use of the transverse frame 159.

With the arrangement illustrated in the accompanying drawings, the ramp128 can be rapidly adjusted to any elevation in the range from 10° abovehorizontal (FIGS. 3 and 4) to 85° above horizontal (FIGS. 5 and 6). Thearrangement can be modified to suit other desired ranges of rampelevation.

The ramp 128 does not directly carry pipe being de-spooled from the mainreel 118, but carries the pipe through the intermediary of a levelwindassembly 160 comprising an elongated frame 162 of rectangularcross-section (see FIG. 14). The levelwind frame 162 is mounted forramp-traversing movement by means of rollers 164 (FIG. 9) running on theramp crossbeams forming the ramp ends 130 and 138. The ramp crossbeams130 and 138 are also fitted with transverse racks 166 engaged byhydraulically-powered pinion/gearbox motor units 167 for controllablydisplacing the levelwind assembly 160 across the ramp 128 as necessaryto ensure correct spooling/de-spooling of pipe onto/off the main reel118 (ie, to ensure "level winding").

The levelwind assembly 160 further includes various items ofpipe-conditioning and pipe-handling equipment which are mounted on theframe 162 for controlling position, movement and shape of pipe passingthrough the levelwind assembly 160. Such equipment includes, by way ofnon-limiting example, a curved main aligner 168 for imparting acontrolled radius to pipe being de-spooled from the main reel 118,pipeline straightening and tensioning means comprising first, second,third and fourth caterpillar track assemblies 170, 171, 172, 173, thefirst, second and third of said assemblies 170, 171, 172 togetherconstituting a "three-roll" pipe straightener, and the third and fourthof said assemblies 172, 173 together constituting a pipe tensioner, atleast one, and preferably a pair, of pipe clamps 174, and a roller frame176 for pipe guidance. The items 168-176 referred to above are known perse, and are described in detail in the above-mentioned WO93/06401 andWO93/06402. Alternative types of straightener, tensioner etc. may besubstituted for those described herein.

The levelwind assembly 160 may also include similar equipment forhandling auxiliary pipe(s) and/or cable(s), for example an auxiliaryaligner 178 and an auxiliary straightener 180.

To facilitate procedures such as pipe inspection, pipe repairs, pipejointing, attachment/removal of haulage couplings to/from the pipe, andother tasks that have to be performed on pipe in passage through thelevelwind assembly 160, the levelwind frame 162 is fitted with a pair ofwork platforms 182 and 184 whose inclinations on the frame 162 areselectively adjustable to allow the platforms 182, 184 to be levelledindependently of the current inclination of the ramp 128 whilecontinuing to facilitate safe and convenient access of personnel to thepipe in that region of the levelwind assembly 160. Access isconveniently enabled by a ladder system and by a man-riding lift, with aseparate system on each side of the levelwind assembly 160. Thelevelwind frame 162 may be shrouded or boxed-in to provide full weatherprotection.

Occasions may arise when it is necessary or desirable to allow the endof a pipe to be let overboard in a controlled manner, or to haul the endof pipe on-board in line with the normal path of continuous pipe. Tomeet these requirements, the vessel 100 is rigged with an "abandonmentand recovery" system (A&R system) 186 which is essentially a winchsystem reeved partly inside the vessel 100 and partly on the levelwindassembly 160. (The version of the A&R system 186 shown in FIG. 9 differsslightly from that shown in FIGS. 1-6, as do certain details of thelevelwind system such as the forward end of the frame 162).

As part of the A&R system 186, a winch 188 is located inside the hull ofthe vessel 100, the winch 188 being anchored on the redundant underdeckstrongpoint originally employed for mounting the DSV sterndeck crane(removed). The A&R rope 190 runs from the winch 188 round a pulley 192anchored between the ramp mountings 124 and 126 up to a pulley orpulleys 194 anchored on the levelwind frame 162 and hence (whendeployed) down the centerline of the levelwind assembly 160 along thesame path as that normally taken by pipe being de-spooled from the mainreel 118. When the A&R system 186 is not required to be operative thepulley or pulleys 194 is/are moved to the side of the levelwindcenterline to be clear of the pipe path (see FIG. 14). The tail of therope 190 on the non-load side of the winch 188 is carried round a pulley196 and onto a take-up drum 198 for tangle-free storage.

The location of the pulley 192 between the ramp mountings 124 and 126has at least two advantages, namely the closer the pulley 192 is tobeing coaxial with the ramp bearings 132 and 134, the closer the A&Rsystem 186 is to being level luffing (ie, to not pulling in or payingout as the ramp elevation changes), and secondly, obstruction of thearea of the deck 136 under the ramp 128 is minimised.

Between the main reel 118 and the large auxiliary reel 120 a combinedpipe/cable bridge and personnel access gangway 200 is cantileveredsternwards off the rear wall of the forward vessel section 102 to passpartly over the main reel 118 at an elevation sufficient to clear pipebeing de-spooled from the reel 118 into the levelwind assembly 160,whatever the current elevation of the ramp 128. The upper side of thebridge/gangway 200 is fitted with lengthwise array of transverse axisrollers 202 to carry auxiliary pipe(s)/cable(s) being de-spooled fromthe large auxiliary reel 120 onto the ramp 128. A pedestrian-carryinggangway (not illustrated) is mounted on the bridge/gangway 200 alongsidethe rollers 202 to allow access from the upper deck of the forwardsection 102 to a location close to and directly over the forward side ofthe hub of the main reel 118. The bridge/gangway 200 is held at theappropriate elevation by means of a strut 204, which may be of a fixedlength to hold the bridge/gangway 200 at a corresponding fixedelevation; alternatively, the strut 204 may be of a controllablyvariable length to hold the bridge/gangway at a selectively variableelevation.

Besides functioning as a combined bridge and gangway, the structure 200gives a measure of protection to the forward section 102 and to thepersonnel therein, by shielding the forward section 102 from theuncontrollable and violent movement of the broken end of pipe should thepipe fracture between the reel 118 and the aligner 168, particularly ifunder considerable tension (which may be as high as 200 Tonnes even whenoperating within design limits).

The dynamic positioning system (DPS) of the original DSV "StenaWellservicer" is retained in the reel pipelaying vessel "Stena ApacheTwo" ("100" in the accompanying drawings). The DPS retained in theconverted vessel 100 comprises three variable-thrust 360°-steerablestern thrusters 206, and three variable-thrust unsteerabletransverse-tunnel bow thrusters 208.

A crane 210 is mounted on the port rail of the vessel 100, aft of themain reel 128 and forward of the small auxiliary reel 122. In-hullfoundations of the crane 210 are partly in the original DSV and partlyin the conversion-added portside sponson 108.

A crane 212 is mounted on starboard rail of the vessel 100, at thefurthest stern of the main deck 136 (FIGS. 1-6 and 7-8). As with theportside crane 210, the in-hull foundations of the starboard crane 212are partly in the original DSV and partly in the conversion-addedstarboard sponson 110. In order to avoid being unduly baulked by thelevelwind assembly 160 at the maximum elevation of the ramp 128, it ispreferred to move the starboard crane further aft from the positionshown in FIGS. 1-6 to the position shown in the modified vessel of FIGS.7 and 8, the starboard sponson 110 and the overlying portion of the maindeck 136 being correspondingly extended sternwards to support therepositioned crane.

Apart from removal of the redundant dive systems, the forward vesselsection 102 retains all the essential features of the forward section ofthe DSV; in addition to the bow thrusters 208, these retained featuresinclude the engine room (not visible), crew accommodation 214, forwardbridge 216, stern bridge 218 (overlooking the main reel 118 and thepipe-launching ramp 128), and helicopter landing deck 220.

Referring now to FIGS. 16, 17 and 18, these show external and internaldetails of a reel-clamping chock 300.

The chock 300 comprises a cylindrical outer casing 302 which is weldedto the main deck 136 through the intermediary of a pair of saddle plates304 and longitudinal reinforcing webs 306. A longitudinally slidablesleeve 308 is mounted within the outer casing 302 by anti-frictionbushes 310 and 312. The reel end of the sleeve 308 is fitted with aflanged plug 314 having an aluminium bronze pad 316 affixed to its outerface.

Extension and retraction of the chock 300 is achieved by a hydrauliccylinder 318 and piston 320 mounted within the sleeve 308. (Hydraulicfluid connections are omitted from FIGS. 16-18 for clarity). The end ofthe hydraulic cylinder 318 remote from the reel-contacting end of thechock 300 is anchored to the casing 302 and hence to the deck 136 by acylinder eye 322 pinned between a pair of U-brackets 324 fixed to theend of the casing 302 by fasteners 326.

The piston 320 is coupled to the reel-contacting end of the chock by apiston eye 328 being pinned to a clevis fitting 330 secured to one endof a pushrod 332. The other end of the pushrod 332 is secured to theinner face of the plug 314.

The reel end of the sleeve 308 is externally screw-threaded with an Acmethread 334. An internally threaded ring 336 is fitted on the sleevethread 334 such that the ring 336 can be selectively positioned alongthe outer end of the sleeve 308 by manually turning the ring 336 aroundthe sleeve 308. The periphery of the ring 336 is drilled with radialholes 338 to enable the ring 336 to be turned by a suitable tool (notshown).

FIG. 16 shows the chock 300 fully extended such that the pad 316forcibly-engages an annular contact surface 222 on the outside end faceof the main reel 118. FIG. 15 also shows the ring 336 screwed up againstthe adjacent end of the sleeve 308 such that reel-clamping forcescontinue to be applied to the reel 118 even if hydraulic pressure isremoved from the cylinder and piston 318 and 320, due to the mechanicallocking of the chock 300 provided by suitably turning the ring 336 onthe sleeve thread 334.

Release of the reel-clamping chock 300 from the fully-applied positionshown in FIG. 16 is achieved by unscrewing the ring 336 until it isclear of the sleeve 308, then applying reversed hydraulic pressure tothe cylinder 318 and piston 320 to pull the movable end of the chock 300away from the main reel 118.

Hydraulic pressure is preferably applied in the reel-clamping directionprior to and during unscrewing of the ring 336 in order to relieve thering 336 of loading which might otherwise hinder or prevent the ring 336being turned.

FIG. 19 is a plan view, to a much reduced scale, of a preferredarrangement for sea fastening, ie, for clamping the main reel 118against axial movement when not spooling or de-spooling (eg, duringtransit to or from a pipe-laying location, or when pipelaying issuspended due to bad weather). An array of four chocks 300 (each asshown in FIGS. 16-18) is secured to the main deck 136 around the lip ofthe reel-holding well 112. One pair of the chocks 300 is disposed toengage the port side of the main reel 118, and the other pair of chocks300 is disposed to engage the starboard side of the main reel 118.Within each of these pairs of chocks 300, one chock is located on oneside of the reel axis and the other chock is located on the other sideof the reel axis, as shown in FIG. 19. This symmetrical array ofreel-clamping chocks ensures inherent equalisation of reel-clampingforces on the reel when the chocks are fed from a common hydraulicsupply, thus avoiding any tendency for the chocks to induce skewing ofthe main reel 118.

Other arrangements of reel-clamping chocks are possible within the scopeof the invention, for example different locations for the chocks and/ordifferent numbers of chocks.

Reel-clamping chocks may also be provided for the large auxiliary reel120 and/or for the small auxiliary reel 122.

FIGS. 20 to 23 show a preferred embodiment of the main reel 400 of areel pipelaying vessel such as that described herein. FIG. 20 shows aside view of the reel 400, whilst FIGS. 21 to 23 show sectional views onlines A--A, B--B and C--C of FIG. 20 respectively.

The reel 400 is of a generally open construction to minimise its weight,and is formed largely from plate steel. A plurality of main spokes 402extend radially outwards from the centre of the reel 400 and have anI-beam type configuration comprising a main planar member 404 and outerand inner planar flanges 406, 408. The outer ends of the spokes 402 areconnected by flange plating 410 which form the sides of thepipe-receiving well 412 of the reel 400. The flange plating 410 isstrengthened by trapezoidal box-section stiffeners 414. The outer andinner edges of the flange plating 410 are further strengthened byknuckles 415, 416. The floor of the well 412 is formed by hub plating418, which is braced by internal stiffeners 420. Intermediate partialspokes 422 are located between each pair of main spokes 402, extendingacross the width of the flange plating 410.

As seen in cross section in FIG. 21, the reel has a "portal frame"configuration, without a main shaft connecting the main rotary bearings423. This configuration improves the fatigue performance of the reel byremoving the additional rigidity and associated stresses caused by thepresence of a continuous shaft as in the original Apache vessel.

In this example, the reel 400 is adapted to be engaged by sea-fasteningchocks, as previously described above, at portions 424 of two of themain spokes 402' on each side of the reel 400. A bracing flange 426extends diagonally between a point adjacent the portion 424 of each ofthe spokes 402' and the adjacent intermediate spoke 422. The portions424 may be formed as anti-friction pads similar to those of the chocksas previously described. This arrangement allows the chocks to beapplied to the reel only when the reel is at a particular angularposition. Accordingly, when the chocks are to be applied, it may benecessary firstly to rotate the reel 400 so as to align the portions 424with the chocks.

FIG. 24 illustrates an alternative arrangement, whereby the chocks maybe applied to the reel at any position. In this case a continuous,annular chock bearing surface 428 extends around the reel, mounted on anextension 430 of the hub plating 418. As is also illustratedschematically in FIG. 24, the contact shoe 432 of the chock may beenlarged in size, in comparison with the previously described embodimentof the chock, presenting a greater contact surface area such that thebearing surface 428 of the reel can be made generally lightweight inconstruction.

FIGS. 25(a), (b) and (c) and FIG. 26 illustrate a preferred arrangementof the pipe clamps 174 previously referred to. FIGS. 3 and 9 show theuse of first and second pipe clamps 174 located on the pipeline pathnear the aft end of the levelwind frame 162. Firstly, it is preferredthat the clamps 174 have a generally cylindrical configuration as shownin FIG. 25, being formed from first and second semi-cylindrical portions450, 452 hinged together along their lengths at 454 below the pipelinepath. Secondly, it is preferred that the clamps be mounted so as to beretractable out of the pipeline path when not in use (as shown in FIG.25(a)). Thirdly, it is preferred that one of the clamps (most preferablythe uppermost clamp closest to the tensioner 172,173) is removable. Themaximum clamping force provided by the two clamps is only likely to berequired in a minority of cases. Accordingly, it desirable that thesecond clamp be removable to provide a greater work space when it is notrequired for a particular operation. If the second clamp is removable,then only a single retractable mounting need be provided for the firstclamp. The mounting will be constructed to be capable of taking thetotal design load of both clamps, and the second clamp may simply beattached to the pipe immediately above the first clamp. This arrangementis schematically illustrated in FIG. 26, where the first clamp isdesignated 174a, the second clamp is designated 174b, the mounting,partially hidden beneath the first clamp, is designated 440, and thepipeline 442 is being unspooled in the direction of the arrow A, theload on the clamp mounting 440 being in the direction of the arrows B.

The clamps may be of the type having a rubber lining and hydraulicpackers as is known in the art. FIG. 25(c) shows the clamp extended andclosed to engage the pipeline, and FIG. 25(b) shows the clamp in anintermediate position between the retracted/open position of FIG. 25(a)and the extended/closed position of FIG. 25(c).

While preferred embodiments of the invention have been described above,the invention is not restricted to these forms, and modifications andvariations of these embodiments can be adopted without departing fromthe scope of the invention.

We claim:
 1. A reel pipelaying vessel, said vessel being fitted with adynamic positioning system, said vessel being provided with areel-holding well at a location amidships, said vessel being providedwith reel-mounting bearings on laterally opposite sides of said well,and said vessel being provided with ramp-mounting bearings at asternwards location on said vessel for the mounting of a pipe-launchingramp thereon, wherein said reel pipelaying vessel further comprises apipe-launching ramp temporarily or permanently mounted on saidramp-mounting bearings, wherein the mounting of said ramp on saidramp-mounting bearings is a rotational mounting whereby the elevation ofthe ramp with respect to the vessel is variable, said ramp havingbearing means at or toward a first end thereof whereby the ramp isrotatably coupled to said ramp-mounting bearings, said vessel furthercomprising ramp elevation control means for controllably varying theelevation of the ramp by rotating an aft end of the ramp about saidrotational mountings, wherein said ramp includes first coupling meanslocated at or toward a second end of the ramp for coupling of the rampto said ramp elevation control means, and wherein said ramp elevationcontrol means comprises variable-length ramp support means anchored ator adjacent one end thereof upon fixed structure of the vessel and at oradjacent the other end of a variable length portion of the support tothe ramp at a location thereon not adjacent said rotational mounting ofsaid ramp, said ramp elevation control means having second couplingmeans for coupling said ramp support means to the first coupling meansor said ramp, the distance between the second coupling means and thefirst end of said ramp support means being variable so as to vary theelevation of the first end of the ramp; wherein said variable-lengthramp support means comprises a pair of rack and pinion elevators, eachcomprising an elongated rack member and a pinion assembly, one of eachpair located one on each side of said ramp and conjointly operable tovary the elevation of said first end of said ramp, and second couplingmeans being provided on said pinion assemblies.
 2. A reel pipelayingvessel as claimed in claim 1, wherein said pipe-launching ramp comprisesa pipe radius control means for imparting a substantially uniform radiuscontrol means for imparting a substantially uniform radius of curvatureto a length of pipe despooled from said reel in pipelaying operation ofsaid vessel.
 3. A reel pipelaying vessel as claimed in claim 1, whereinsaid pipe-launching ramp comprises level-wind means for accommodatingvariations in the lateral positioning of a length of pipe spooled ontosaid reel as a plurality of side-by-side turns, during spooling andde-spooling of said length of pipe.
 4. A reel pipelaying vessel asclaimed in claim 3, wherein said level-wind means and said pipe radiuscontrol means are mounted and controlled for conjoint lateral movement.5. A reel pipelaying vessel as claimed in claim 5, wherein said piperadius control means is mounted upon said level-wind means for carriagethereby.
 6. A reel pipelaying vessel as claimed in claim 3, wherein saidramp includes at least two levelwind-mounting crossbeams, said levelwindmeans comprising a rectangular lattice mounted for lateral movement onsaid crossbeams, lateral movement control means for laterally movingsaid lattice on said crossbeams, radius control means carried on saidlattice for imparting a uniform curvature to a pipe being despooled oversaid ramp, and pipe gripping means carried by said lattice for ripping apipe being de-spooled over said ramp to apply straightening andtensioning forces to said pipe.
 7. A reel pipelaying vessel as claimedin claim 6, wherein the lattice is boxed in or surrounded to providefull weather protection.
 8. A reel pipelaying vessel as claimed in claim6, wherein the lattice is equipped with a dual bulkhead/platform systemto provide a working location which allows personnel to work on thelattice whether the ramp is near horizontal or near vertical.
 9. A reelpipelaying vessel as claimed in claim 1, including a pipe-spooling reel,wherein said pipe-spooling reel includes first and second lateral sideportions each comprising a central rotary bearing, a plurality of radialspokes extending outwardly from said central rotary bearing and a mainflange surface connecting at least the outer portion of said spokes, thereel further including a hub surface connecting said lateral sideportions such that said reel, in radial cross-section, has a portalframe configuration, there being no central shaft connecting the rotarybearing of the respective side portions.
 10. A reel pipelaying vessel asclaimed in claim 1, further including pipeline clamping means locatedadjacent the aft end of a pipe-launching ramp, said clamping meanscomprising at least a first clamp of generally cylindrical configurationmounted on said ramp by clamp mounting means, said first clampcomprising first and second semi-cylindrical portions hinged togetheralong their lengths on a side of the clamp disposed below the pipelinepath, and wherein said clamp mounting means has a load capacity greaterthan the load capacity of said first clamp, whereby the clamp loadcapacity may be increased up to the capacity of said clamp mountingmeans by securing one or more additional clamps to the pipeline inabutment with the first clamp and, upstream therefrom in the directionof pipeline unspooling.
 11. A reel pipelaying vessel as claimed in claim10, wherein said clamp mounting means is adapted to be retractable suchthat said first clamp may be retraced to a position below the pipelinepath when not in use.
 12. A reel pipelaying vessel as claimed in claim1, wherein said pipe-launching ramp further includes pipe gripping meansfor gripping a pipe being de-spooled over said ramp to applystraightening and tensioning forces to said pipe.
 13. A reel pipelayingvessel, said vessel being fitted with a dynamic positioning system, saidvessel being provided with a reel-holding well at a location amidships,said vessel being provided with reel-mounting bearings on laterallyopposite sides of said well, said vessel being provided withramp-mounting bearings at a sternwards location on said vessel for themounting of a pipe-launching ramp thereon and further comprising apipe-launching ramp temporarily or permanently mounted on saidramp-mounting bearings, wherein the mounting of said ramp is arotational mounting whereby the elevation of the ramp with respect tothe vessel is variable and said vessel further comprises ramp elevationcontrol means for controllably varying the elevation of the ramp, andwherein the combination of said pipe-launching ramp and saidramp-mounting bearing is such that the underside of said pipe-launchingramp is clear of underlying deck of the reel pipelaying vessel, at leastbetween said ramp-mounting bearings and such part or parts of the deckat which said-ramp elevation control means is anchored.
 14. A reelpipelaying vessel as claimed in claim 13, wherein the deck to rampunderside clearance is preferably at least sufficient to constitutewalk-under headroom.
 15. A reel pipelaying vessel as claimed in claim13, wherein said ramp-mounting bearings are arranged to dispose ahorizontal pivot axis for the ramp substantially above said underlyingdeck whereby thus to provide at least the greater part of saidclearance.
 16. A reel pipelaying vessel as claimed in claim 13, whereinsaid ramp elevation control means comprises variable-length ramp supportmeans anchored at or adjacent one end thereof upon fixed structure ofthe vessel and at or adjacent the other end of a variable length portionof the support to the ramp at a location thereon not adjacent saidrotational mounting of said ramp.
 17. A reel pipelaying vessel asclaimed in claim 16, wherein said variable-length ramp support meanscomprises a pair of rack and pinion elevators, one of each pair locatedon each side of said ramp and conjointly operable to vary the elevationof said ramp with respect to said vessel.
 18. A reel pipelaying vessel,said vessel being fitted with a dynamic positioning system, said vesselbeing provided with a reel-holding well at a location amidships, saidvessel being provided with reel-mounting bearings on laterally oppositesides of said well, and said vessel being provided with ramp-mountingbearings at a sternwards location on said vessel for the mounting of apipe-launching ramp thereon, wherein said reel pipelaying vessel isprovided with restrain means selectively operable on at least a mainpipe reel to provide at least lateral restraint of said main reel whilesaid main reel is not required to rotate, whereby to relieve the reelbearings of at least some lateral loading when said restraint means isapplied.
 19. A reel pipelaying vessel as claimed in claim 18, whereinsaid restraint means comprises an array of chocks which can beselectively pressed against or retracted from opposite sides of the reelon either side of the rotation axis thereof whereby selectively to applylateral clamping forces on the reel.
 20. A reel pipelaying vessel asclaimed in claim 19, wherein each chock comprises a hydraulicallyextendable strut lockable in its extended condition by means of ascrew-threaded fastener.
 21. A reel pipelaying vessel as claimed inclaim 19, wherein each said chock is anchored at one end thereof to atleast one of the reel-holding well and to vessel decking adjacentthereto.
 22. A reel pipelaying vessel as claimed in claim 21, whereineach said chock is preferably provided at the other end thereof with areel-contacting surface of reduced friction.
 23. A reel pipelayingvessel as claimed in claim 19, wherein said reel is adapted to beengaged by said chocks at a plurality of predetermined locations.
 24. Areel pipelaying vessel as claimed in claim 19, wherein said reel isprovided with a continuous, annular bearing surface on either lateralside thereof, said bearing surface being adapted to be engaged by saidchocks at any portion thereof regardless of the rotational position ofthe reel.
 25. A reel pipelaying vessel as claimed in claim 19, whereineach of said chocks comprises a power-extendable jack, selectivelyoperable locking means for locking said jack in an extendedconfiguration thereof, coupling means at one end of the chock forcoupling that end of the chock to an anchorage, and reel contactingmeans at the other end of the chock for the application of jacking forceto said reel.
 26. A reel pipelaying vessel as claimed in claim 25,wherein said power-extendable jack is a hydraulic jack.
 27. A reelpipelaying vessel as claimed in claim 25, wherein said selectivelyoperable locking means comprises a screw-threaded nut or an internallyscrew-threaded ring which can be screwed along one part of said jack,after extension of said jack, to bear against another part of said jackwhich has been extended relative to said one part of said jack wherebyto lock said two parts against relative movement tending to reverse suchextension.
 28. A reel pipelaying vessel as claimed in claim 25, whereinsaid reel-contacing means comprises a friction-reducing means forcontacting the reel in use for the chock.
 29. A reel pipelaying vesselas claimed in claim 28, wherein said friction-reducing means comprises abronze pad attached to or integral with said other end of the chock. 30.A reel pipelaying vessel as claimed in claim 11, said array of chockscomprising at least four reel-clamping chocks disposed so that arespective plurality of said chocks is extendable to contact each of theaxially opposite ends of the reel, with at least one chock in each saidplurality being disposed to be extendable to contact the respective endof the reel at a location thereon which is substantially diametricallyopposite to a location on that end of said reel to which at least oneother chock in the same plurality is extendable to contact that end ofsaid reel, wherein said array may be operated in a manner to reduce oreliminate skewing forces imposed on said reel by application thereto ofreel-clamping force.
 31. A reel pipelaying vessel, said vessel beingfitted with a dynamic positioning system, said vessel being providedwith a reel-holding well at a location amidships, said vessel beingprovided with reel-mounting bearings on laterally opposite sides of saidwell, and said vessel being provided with ramp-mounting bearings at asternwards location on said vessel for the mounting of a pipe-launchingramp thereon, wherein said reel pipelaying vessel is provided with oneor more auxiliary reels for the spooling/de-spooling of at least one ofcable(s) and auxiliary pipe(s), wherein at least one auxiliary reel islocated forward of the main pipe reel, and wherein said pipelayingvessel is provided with a bridging structure leading auxiliarypipe/cable to/from the at least one auxiliary reel from/to thepipe-launching ramp in a path extending over and clear of the path ofpipe between said ramp and the main reel.
 32. A reel pipelaying vesselas claimed in claim 31, wherein said fixed cantilever or other bridgingstructure is provided with an array of rollers or other suitable meansfor facilitating passage of the auxiliary pipe/cable thereover.
 33. Areel pipelaying vessel as claimed in claim 31, wherein said auxiliaryreel(s) are laterally aligned with the main pipe reel, and locatedsubstantially on the longitudinal centre-line of the vessel fore or aftof the main pipe reel.
 34. A reel pipelaying vessel as claimed in claim31, wherein, where the auxiliary reel or at least one of the auxiliaryreels carries or is intended to carry a plastically deformable auxiliarypipe or cable, the pipe-launching ramp is formed with or provided with arespective auxiliary radius control means for imparting a substantiallyuniform radius of curvature to said auxiliary pipe or cable.
 35. A reelpipelaying vessel, said vessel being fitted with a dynamic positioningsystem, said vessel being provided with a reel-holding well at alocation amidships, said vessel being provided with reel-mountingbearings on laterally opposite sides of said well, and said vessel beingprovided with ramp-mounting bearings at a sternwards location on saidvessel for the mounting of a pipe-launching ramp thereon, wherein thevessel is further equipped with an abandonment and recovery systemcomprising a winch arrangement extending a haulage wire from a suitablylocated winch by way of one or more sheaves to extend down apipe-launching ramp so as to enable the end of a pipe being laid to belet overboard in a controllable fashion, and to facilitate the pullingon-board of a pipe end, wherein a winch haulage drum is anchored withinthe vessel forward of the ramp-mounting bearings, and wherein the wincharrangement includes one sheave located adjacent the ramp-mountingbearings to give the abandonment and recovery system a measure of levelluffing, and at least one further sheave disposed on the ramp at alocation substantially displaced from the sternwards end of the ramp,said haulage wire extending aft from said winch haulage drum, aroundsaid one sheave, forward from said one sheave and around said furthersheave to bring the haulage wire into a path extending down the rampfrom said location on the ramp.
 36. A reel pipelaying vessel as claimedin claim 35, wherein the sheaves have articulated anchorage to cope withlevel winding traverses and variable ramp elevations.
 37. A reelpipelaying vessel as claimed in claim 35, wherein the sheaves arewide-bodied to allow the passage of wife rope fittings and shacklesincorporated into the abandonment and recovery system.